It is normal practice to test hydraulic pumps and motors under simulated working conditions after repairs are made thereto to ensure that they meet the rated specifications. Such hydraulic pumps and motors are currently tested on test benches by loading the pump and motors through a relief valve. These test benches commonly use an electric motor as the source of power. One of the problems encountered with that type of testing is that the test is limited to the direct input horsepower capacity of the electric drive motor. To provide an electric motor having sufficient horsepower to test many of today's high pressure, high volume pumps and motors is not feasible because of the size and cost of such high horsepower electric motors. Moreover, dumping the high volume of fluid across a relief valve at high pressure generates heat which would then necessitate the addition of large coolers to keep the oil cooled to the proper operating temperature.
One solution to the above problem is disclosed in U.S. Pat. No. 4,368,638 wherein the test bench has power regeneration features. The test bench thereof includes a primary power source which drives a gear train to which both a hydraulic pump and a hydraulic motor are mechanically connected. The hydraulic pump is driven by the gear train and transmits fluid to the hydraulic motor which converts the fluid pressure to mechanical power which is then used to drive the gear train. A disadvantage of such system is that the gear train would also take up considerable space and would have inherent frictional losses. Another disadvantage is that the pump and motor must run at the same speed such that the test bench could only be used to test pumps and motors at the normal operating speed of the gear train.
The present invention is directed to overcoming one or more of the problems as set forth above.